An absorbent article normally comprises an upper liquid-permeable sheet, an absorbent sheet, and a bottom liquid-impermeable barrier sheet, said sheets being delimited by two transverse edges and two longitudinal edges. The article includes a front part and a rear part between which there extends a crotch part that has a wetting region within which the major part of the body fluid is delivered. The absorbent sheet, or layer, will often include a superabsorbent material.
The superabsorbent material is present in particle form, e.g. in a grain, granule, flake or fibre form, and is mixed or layered with other absorbent material, normally cellulose fibres. Superabsorbent materials are polymers that are able to absorb such liquid as water and body fluids, e.g. urine and blood, while swelling and forming a gel that will not dissolve in water. Some superabsorbent materials are able to retain absorbed liquid even when subjected to external pressures. These materials have been used widely in absorbent sanitary products, such as diapers, sanitary napkins, incontinence protectors and like products.
The effectiveness of a superabsorbent material is contingent on many factors, such as how it is mixed into the absorbent structure, its particle form and particle size, and also its physical and chemical properties such as absorption rate, gel strength and liquid retention properties. The absorption capacity of a superabsorbent can be influenced negatively by a phenomenon known as gel blocking. Gel blocking is when the superabsorbent material forms a gel that blocks the pores in the fibre structure or the particle interstices when the absorbent article is wetted. Such blocking impedes the transportation of liquid from the wetted area out to the remainder of the absorbent body and will prevent the total absorption capacity of the absorbent body from being fully utilised and also creates a leakage risk.
With the intention of abating the problem caused by gel blocking, it is known, e.g., to use superabsorbent particles that are embraced by a casing which is only slowly dissolved in and/or penetrated by the liquid to be absorbed, such as to impart to the superabsorbent material a delayed activation time. Prior publication WO 95/00183 teaches an absorbent article that has an absorbent structure which includes superabsorbent material having a delayed activation time in the wetting region of the structure, and conventional superabsorbent material in those regions that lie outside this wetting region.
The problem of gel blocking can also be reduced by using a superabsorbent material that has a high gel strength. High gel strength superabsorbent materials are able to retain absorbed liquid when the swollen material is subjected to external loads, and is also able to absorb a significant quantity of liquid when subjected to external loads. EP 0 339 461 describes a high gel strength superabsorbent for use in absorbent articles. This superabsorbent is able to retain its form to a large extent and will not collapse when swelling.
EP 0 532 002 teaches a superabsorbent material of high gel strength that also has a certain liquid dispersion capacity.
Thus, as described above, one problem with absorbent articles that include superabsorbent material is gel blocking. This increases the risk of leakage and prevents the total capacity of the absorbent structure from being fully utilised. Another drawback with conventional superabsorbents is found in the large extent to which they swell. High concentrations of superabsorbent can swell into a large clump at the wetting point, so as to cause discomfort to the wearer after wetting the article.
The object of the present invention is to provide a solution to these problems.